Polyolefins such as high density polyethylene (HDPE) homopolymer and linear low density polyethylene (LLDPE) copolymer can be produced using various combinations of catalyst systems and polymerization processes. Traditional chromium-based catalyst systems can produce olefin polymers having, for example, good extrusion processibility and polymer melt strength, typically due to their broad molecular weight distribution (MWD). In some end-use applications, it can be beneficial for the olefin polymer also to have lower levels of long chain branching. Moreover, it can be beneficial for the catalyst system employed to have a high catalytic activity for olefin polymerization, as well as a greater potential for a broader range of polymer melt index and molecular weight. Accordingly, it is to these ends that the present invention is directed.